As far as I'm aware, I don't know of a single incidence where MD's have opted for life-saving interventions for a baby younger than about 23 weeks. This is usually the minimum allowable growth before an infant is considered 'compatible with life'. Any younger than that and their bodies simply aren't formed enough to live, even with support like ventilators, etc. Depending on the baby's particular circumstances, 23-24 weeks is the usual BARE MINIMUM date for viable delivery, and even then, you are opening the situation up to a number of endings, not all of them good- severe lung disease, infection, neurological disorders (some of them profound), etc. The doctors, in these cases, will attempt to prolong the pregnancy as long as feasible- the longer the baby is in mom, the chances for survivial and a certain quality of life improve (statistically, anyway). If the baby is a danger to mom, the pregnancy will usually be terminated, even at such a 'late' stage.
This web site can give you more information regarding chances for survival:
As you can see, a baby born at 21 weeks has an estimated 0% chance of survival. One week later, the chance rises to an estimated 10%. By the 23 week, the chance for survival jumps from an estimated max of 10% to 40%. That's an almost 50% increase in a mere two weeks more of pregnancy. I hope and pray, for her and her family, that she and her baby manage to hang in there, and though it is of little comfort to someone in such a horrible and heart-wrenching situation, they will be in my thoughts.
I'm terribly sorry for your friend. She'll be in my prayers tonight.